1. Field of the Invention
The present invention relates to a system for making a diagnosis whether there is failure in a fuel gas purge system for purging (discharging) fuel evaporative gas adsorbed in a canister to an intake pipe of an internal combustion engine.
2. Description of the Related Art
In a conventional failure diagnostic device of a fuel gas purge system, conditions on which a purge-execution-integrated time or an integrated purge amount after starting of the internal combustion engine reaches a predetermined value are added to failure diagnostic conditions. These additional conditions are used to judge whether or not the canister is sufficiently purged, and failure diagnosis is made when an amount of fuel evaporative gas remaining in the canister is sufficiently small. This prevents production of an over-rich mixture caused by fuel evaporative gas flowing into the intake pipe during the failure diagnosis, thereby preventing deterioration in drivability and emission (for example, see the Japanese Patent Publication (unexamined) No. 1997-177617). Another conventional failure diagnostic device of a fuel gas purge system of the same type is disclosed in, for example, the Japanese Patent Publication (unexamined) No. 1999-22564.
In the mentioned conventional failure diagnostic device of a fuel gas purge system, however, when detection of malfunction is once interrupted for any reason and carried out again, the resumed purge takes the same time as long as the purge-execution-integrated time of the canister. Hence a problem exists in that it is not possible to carry out detection of malfunction at a higher frequency.